If the sentence in question is a statement (ends with a period), I would probably "however" as your transition word.
A. Carefully read the directions
The test will contain any directions about how to complete it. This is where any special information will be contained. Sometimes teachers will put directions about the format of the test and how to complete it on the study guide, but this isn't always true. A classmate is not necessarily a reliable source and, similar to the study guide, cannot be utilized when taking the test. Option D is also not a good choice since the test directions will have any special information about how to complete the test.
